Inside my case.yml I have not specified any relation.
How would I do this? As I have no relation specified in a case I am not sure what the best (kirby) way is to accomplish this. I found this: Filtering compendium | Kirby CMS
Long answer:
i created a few issues at the repo as well all related to the fact that kql is limited in use without being extendable but development seems to have stopped for now. kirby 3.6.0 is keeping everyone busy.
I see, thanks. As this is a rather small application with just a few items and not used in public I will just create a second query and filter the results on nodeJS side. I will look into the interceptors anyway though.